Britain's ability to recover from its deepest postwar recession moved to the heart of the election campaign today when Gordon Brown and David Cameron clashed over news that the economy had grown by a weaker than expected 0.2% in the first three months of 2010.

Brown said the Conservatives had got every big call wrong during the three-year financial crisis, claiming Cameron's plans to cut spending by £6bn in an emergency June budget would push the UK back into a double-dip recession.

The prime minister said cutting spending now would be a "death sentence for thousands of jobs", taking money out of the economy when it was needed most.

"It is the wrong decision, they have the wrong values, it leads them again to the wrong calls," he said.

Cameron said the real threat to Britain's economic prospects was the increase in national insurance contributions planned for next April.

The Conservative leader said voters faced a big choice, adding: "Labour say the economy will collapse unless they keep on wasting your money. We say this jobs tax will kill the recovery.

"Real growth only comes when make it easier for people ... to start a business, take people on and grow. So we're going to cut Labour's waste to stop their jobs tax."

The row came following the release of the last important economic data before the election on 6 May.

After growing by 0.2% in the last quarter of 2009, the economy's pace of growth halved in the first three months of the year.

Vince Cable, the Treasury spokesman for the Liberal Democrats, said the economy was at risk of a double-dip recession even without spending cuts.

And speaking to the Guardian from Washington, the chancellor, Alistair Darling, said Cameron would be forced to axe jobs in order to cut public spending.

"Confidence is everything," Darling said. "If you break that confidence, you run the risk of going back into recession.

"The recovery is still fragile. To start taking money [out of the economy] now would be madness. If we derail the recovery, all the progress we have made will have been for nothing."

Darling warned that the psychological impact of the Tory cuts would be far greater than their monetary value.

"Our stimulus package was worth £6bn, but the impact on confidence would be far greater," he said. "It would be the same with the Tory cuts, which would come in a quarter of the way through the year and would inevitably fall on jobs."

Economists said the gross domestic product (GDP) growth figure was likely to be revised higher when the Office for National Statistics (ONS) issued two more detailed estimates, in May and June, after it had collated more data.

There were signs that the harsh weather at the start of the year had hurt growth as restaurants, shops and building companies lost business.

Hetal Mehta, a senior economic adviser to the Ernst & Young Item Club, said: "It does seem that, following the bounceback in February from the fall in output in January, momentum in the economy is waning.

"Downside risks to economic growth remain, not least the extent of the fiscal tightening we will see after the election."

On the campaign trail, Brown increased the pressure on the Tories over the economy.

Speaking at a college in Coventry, he saidd that the government's economic interventions had staved off a deeper recession.

He compared Labour's record to that of the Conservatives, who he said had argued for a "different, and a more dangerous course", adding: "That is the scale of risk these people present in the economy."

Cable said the figures showed "the promised recovery is barely visible" and rounded on the Tory plans for spending cuts.

"As people deal with their own debts, and as the banks continue to strangle good British businesses by starving them of credit, the recovery will remain fragile," he warned.

"The British economy has had a massive heart attack – it has just emerged from the intensive care unit into the recovery ward.

"The worst possible action is the Tory proposal to pull out the dripfeed when the patient is still in a critical condition."

"What Britain doesn't need now is a jobs tax that would kill the recovery or a hung parliament that would lead to economic paralysis," he said.

"What we need is a new government ready to take decisive action to stop the jobs tax, deal with our debts and get the economy working for everyone."

The ONS echoed business surveys blaming the harsh weather, saying there was anecdotal evidence that it had depressed output from the retail sector and industry.

The service sector – which ranges from shops to banking – grew at less than half the 0.5% pace recorded in the final three months of 2009.

Darling said he had not been surprised by the sluggish economic performance between January and March.

"A lot of the stimulus measures designed to bring spending forward into 2009 came off, so it was in line with what I had been expecting," he added. "I still believe the economy will grow by between 1% and 1.5% this year."

The chancellor said here was a good chance that the early estimate of GDP for the first quarter would be revised later, noting that growth in the final three months of 2009 had been pushed up from 0.1 to 0.4% once more data was available to the ONS.

But he said recovery was not being aided by the weak performance of the eurozone, the destination for more than half of Britain's manufactured exports.